1 files changed, 14 insertions, 0 deletions
diff --git a/src/nwc-lock.js b/src/nwc-lock.js
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+++ b/src/nwc-lock.js
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+// One request, one answerer per origin.
+//
+// Every open tab of the same wallet (and its service worker) sees every NWC
+// request. Without exclusion two hidden tabs on one laptop both paid a zap:
+// the loser's "payment already in progress" error reached the client half a
+// second before the winner's preimage, and the zap showed as failed while
+// the sats had gone. Web Locks are shared by every same-origin context, so
+// the first to claim a request's lock answers it and the rest stay quiet.
+// Where locks are unavailable (tests, ancient engines) the caller just runs.
+export async function withRequestLock(id, fn, held = () => undefined) {
+  const locks = typeof navigator !== 'undefined' && navigator.locks;
+  if (!locks || !id) return fn();
+  return locks.request(`nwc-req:${id}`, { ifAvailable: true }, (lock) => (lock ? fn() : held()));
+}